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Potential Successful Linux RDP Brute Force Attack Detected

Elastic Stack Serverless Security

An RDP (Remote Desktop Protocol) brute force attack involves an attacker repeatedly attempting various username and password combinations to gain unauthorized access to a remote computer via RDP, and if successful, the potential impact can include unauthorized control over the compromised system, data theft, or the ability to launch further attacks within the network, jeopardizing the security and confidentiality of the targeted system and potentially compromising the entire network infrastructure. This rule identifies multiple consecutive authentication failures targeting a specific user account within a short time interval, followed by a successful authentication.

Rule type: eql

Rule indices:

  • auditbeat-*
  • logs-auditd_manager.auditd-*

Severity: medium

Risk score: 47

Runs every: 5m

Searches indices from: now-9m (https://www.elastic.co/guide/en/elasticsearch/reference/current/common-options.html#date-math[Date Math format], see also Additional look-back time)

Maximum alerts per execution: 100

References: None

Tags:

  • Data Source: Auditd Manager
  • Domain: Endpoint
  • OS: Linux
  • Use Case: Threat Detection
  • Tactic: Credential Access
  • Resources: Investigation Guide

Version: 8

Rule authors:

  • Elastic

Rule license: Elastic License v2

Investigation guide

Triage and analysis

[TBC: QUOTE]
Investigating Potential Successful Linux RDP Brute Force Attack Detected

Remote Desktop Protocol (RDP) enables users to connect to and control remote systems, often used for administrative tasks. Adversaries exploit RDP by attempting numerous login attempts to gain unauthorized access, potentially leading to data breaches or further network infiltration. The detection rule identifies a pattern of failed login attempts followed by a successful one, indicating a possible brute force attack, thus alerting security teams to investigate and mitigate the threat.

Possible investigation steps

  • Review the authentication logs on the affected Linux host to identify the specific user account targeted by the failed and successful login attempts, focusing on entries with event.action as "authenticated" and auditd.data.terminal containing "rdp".
  • Analyze the source IP addresses associated with the failed and successful login attempts to determine if they originate from known or suspicious locations.
  • Check for any unusual activity or changes on the compromised system following the successful login, such as new user accounts, modified files, or unexpected network connections.
  • Correlate the timestamps of the authentication events with other security logs to identify any concurrent suspicious activities or anomalies within the network.
  • Investigate the user account’s recent activity and permissions to assess potential impacts and determine if the account has been used for unauthorized access or lateral movement within the network.
  • Evaluate the risk score and severity of the alert in the context of the organization’s security posture and prioritize response actions accordingly.

False positive analysis

  • Legitimate administrative activities may trigger the rule if administrators frequently log in using RDP for system management. To handle this, create exceptions for known administrator accounts or IP addresses that regularly perform these tasks.
  • Automated scripts or services that use RDP for routine operations can cause false positives. Identify these scripts and whitelist their associated user accounts or IPs to prevent unnecessary alerts.
  • Scheduled tasks or cron jobs that involve RDP connections might be misinterpreted as brute force attempts. Exclude these tasks by specifying their user accounts or terminal identifiers in the rule configuration.
  • Security testing or penetration testing activities can mimic brute force patterns. Coordinate with security teams to exclude these activities during testing periods by temporarily adjusting the rule parameters or adding exceptions for testing IP ranges.

Response and remediation

  • Immediately isolate the affected Linux host from the network to prevent further unauthorized access or lateral movement by the attacker.
  • Reset the compromised user account’s password and any other accounts that may have been accessed using the same credentials to prevent further unauthorized access.
  • Conduct a thorough review of the affected system for any signs of additional compromise, such as unauthorized software installations or changes to system configurations, and remove any malicious artifacts.
  • Implement multi-factor authentication (MFA) for RDP access to enhance security and reduce the risk of future brute force attacks.
  • Review and tighten firewall rules to restrict RDP access to only trusted IP addresses and consider using a VPN for remote access.
  • Monitor the network for any unusual activity or further attempts to exploit RDP, using enhanced logging and alerting mechanisms.
  • Escalate the incident to the security operations center (SOC) or relevant security team for further investigation and to ensure comprehensive remediation and recovery actions are taken.

Setup

Setup

This rule requires data coming in from one of the following integrations: - Auditbeat - Auditd Manager

Auditbeat Setup

Auditbeat is a lightweight shipper that you can install on your servers to audit the activities of users and processes on your systems. For example, you can use Auditbeat to collect and centralize audit events from the Linux Audit Framework. You can also use Auditbeat to detect changes to critical files, like binaries and configuration files, and identify potential security policy violations.

The following steps should be executed in order to add the Auditbeat on a Linux System:

  • Elastic provides repositories available for APT and YUM-based distributions. Note that we provide binary packages, but no source packages.
  • To install the APT and YUM repositories follow the setup instructions in this helper guide.
  • To run Auditbeat on Docker follow the setup instructions in the helper guide.
  • To run Auditbeat on Kubernetes follow the setup instructions in the helper guide.
  • For complete “Setup and Run Auditbeat” information refer to the helper guide.

Auditd Manager Integration Setup

The Auditd Manager Integration receives audit events from the Linux Audit Framework which is a part of the Linux kernel. Auditd Manager provides a user-friendly interface and automation capabilities for configuring and monitoring system auditing through the auditd daemon. With auditd_manager, administrators can easily define audit rules, track system events, and generate comprehensive audit reports, improving overall security and compliance in the system.

The following steps should be executed in order to add the Elastic Agent System integration "auditd_manager" on a Linux System:

  • Go to the Kibana home page and click “Add integrations”.
  • In the query bar, search for “Auditd Manager” and select the integration to see more details about it.
  • Click “Add Auditd Manager”.
  • Configure the integration name and optionally add a description.
  • Review optional and advanced settings accordingly.
  • Add the newly installed “auditd manager” to an existing or a new agent policy, and deploy the agent on a Linux system from which auditd log files are desirable.
  • Click “Save and Continue”.
  • For more details on the integration refer to the helper guide.

Rule Specific Setup Note

Auditd Manager subscribes to the kernel and receives events as they occur without any additional configuration. However, if more advanced configuration is required to detect specific behavior, audit rules can be added to the integration in either the "audit rules" configuration box or the "auditd rule files" box by specifying a file to read the audit rules from. - For this detection rule no additional audit rules are required to be added to the integration.

Rule query

sequence by host.id, related.user with maxspan=5s
  [authentication where host.os.type == "linux" and event.action == "authenticated" and
   auditd.data.terminal : "*rdp*" and event.outcome == "failure"] with runs=10
  [authentication where host.os.type == "linux" and event.action  == "authenticated" and
   auditd.data.terminal : "*rdp*" and event.outcome == "success"] | tail 1

Framework: MITRE ATT&CKTM